This project examines the epidemiology of periodontal disease. One investigation examines the patterns of disease progression and behavioral, immunologic, and clinical risk factors for early-onset periodontitis, a disease characterized by a progressive loss of the tooth supporting tissue in adolescents and young adults. Another investigation addresses gaps in existing knowledge about the prevalence, distribution, and patterns of infection by Actinobacillus actinomycetemcomitans (Aa) and Porphyromonas gingivalis (Pg), two microbial species in the subgingival dental plaque microflora that have been strongly implicated in the pathogenesis of periodontitis. In this study, the patterns of serum antibodies to these pathogens are being examined in a large representative sample of the U.S. population to: determine the prevalence of elevated serum antibodies to Aa and Pg, examine the distribution of infection (i.e., variation in elevated antibody titers) among selected demographic groups, and to correlate antibody titers with clinical disease patterns. The results of this study may help identify subgroups of the population who have an especially high prevalence of elevated titers or an excess risk of periodontal consequences of infection. Identification of high risk groups may also be useful for designing effective targeted prevention programs. The focus of the third study, the oral research component of the Baltimore Longitudinal Study of Aging, is to assess behavioral, medical and physiologic determinants of linear changes in radiographic alveolar bone height and to validate for quality assurance, the radiovisiography, a direct digital imaging system, for use in the measurement of alveolar bone loss. The relative importance of biological, sociodemographic, economic, attitudinal, and care-seeking factors in explaining the reasons for tooth extraction is the focus of another study involving patients in dental practices in North Carolina and Connecticut. Understanding the role of these factors is important for identifying groups at high risk of extraction of salvageable teeth and for designing effective prevention efforts.